1. Field of the Invention
The present invention relates to a method and a system for component positioning used during assembly of a scroll-type fluid machine which is incorporated in such an apparatus as a refrigerator, an air conditioner or a vacuum pump. More particularly, the invention is concerned with a method and a system for positioning a stationary scroll when fixing the same to a frame in combination with an orbiting scroll.
2. Description of the Background Art
Conventionally, a process of assembling a scroll-type fluid machine requires a step of centering a stationary scroll. For example, a process of assembling a scroll-type fluid machine includes the steps of assembling a compliant frame in a guide frame, inserting a rotary shaft into a rotary shaft bearing formed in the compliant frame, engaging an Oldham coupling with Oldham guide grooves formed in the compliant frame, and assembling an orbiting scroll with the compliant frame with the Oldham coupling placed in between such that an eccentric shaft end portion formed at one end of the rotary shaft is fitted in an eccentric shaft end bearing formed in the orbiting scroll. Subsequently, a stationary scroll is assembled with the orbiting scroll and fixed in position by tightening bolts. In this assembling process, the stationary scroll is positioned with respect to the guide frame by fitting reamer pins in reamed holes formed in both the guide frame and the stationary scroll. Japanese Patent No. 3287573 describes an example of this kind of stationary scroll positioning method using reamer pins and an assembly method for assembling a scroll-type fluid machine.
On the other hand, Japanese Patent Application Publication No. 2001-221170 describes another kind of stationary scroll positioning method which does not require any reamer pins. According to this Publication, the stationary scroll positioning method is used in a process of assembling a scroll-type fluid machine from a semifinished assembly which has been prepared by assembling an orbiting scroll having a spiral-shaped wall, or scroll wrap, and a rotary shaft for turning the orbiting scroll in a frame in such a manner that the orbiting scroll can produce orbital motion and the rotary shaft is supported from a radial direction, and arranging a stationary scroll having a spiral-shaped scroll wrap in such a manner that the scroll wraps of the stationary scroll and the orbiting scroll are intermeshed and the stationary scroll can move relative to the frame. This stationary scroll positioning method includes the steps of:
(a) holding the frame of the aforementioned semifinished assembly;
(b) turning the rotary shaft while applying a horizontal thrust such that the rotary shaft inclines;
(c) pressing the stationary scroll against the frame under specific pressure while the rotary shaft turns;
(d) measuring displacements of the stationary scroll in individual horizontal directions from at least two directions when the rotary shaft turns;
(e) evaluating stability of an orbital path of the stationary scroll based on the displacements of the stationary scroll in the individual horizontal directions measured in step (d) above; and
(f) determining a fixing point on which the stationary scroll is to be fixedly centered with respect to the frame if the orbital path of the stationary scroll is judged to be stable in step (e) above based on the displacements measured in step (d) above.
Generally, in a scroll-type fluid machine used as a compressor, a stationary scroll and an orbiting scroll must be arranged with high precision in accordance with a prescribed geometrical arrangement scheme such that a smoothly changing clearance is created between scroll wraps of the two scrolls, thus forming a series of pockets (compression chambers) from one contact point of the scroll wraps to the next. If the stationary and orbiting scrolls are not intermeshed with such high precision, it will be impossible to achieve high performance and reliability of the compressor due to poor fluid tightness of the compression chambers.
It is usually impossible to create such a smoothly changing clearance between the scroll wraps of the stationary and orbiting scrolls by using the conventional positioning method and assembly method described in Japanese Patent No. 3287573 as a result of dimensional errors occurring in machining the scroll wraps or poor accuracy of machining central parts of the scroll wraps and the reamed holes. Additionally, machining cost necessary for making the reamed holes and materials cost needed for the reamer pins would lead to an overall cost increase.
While the stationary scroll positioning method of Japanese Patent Application Publication No. 2001-221170 is intended to solve the aforementioned problems discussed with reference to the stationary scroll positioning method of Japanese Patent No. 3287573 using the reamer pins, the positioning method of the former Publication has disadvantage which are described below. In the semifinished assembly prepared in the process of assembling the scroll-type fluid machine of Japanese Patent Application Publication No. 2001-221170, both the frame (which may include not only a guide frame but also a compliant frame if provided) in which a rotary shaft bearing is formed and a sub-frame in which a secondary shaft end bearing is formed are fixed in an outer cylinder (or shell having a cylindrical shape) of the scroll-type fluid machine in advance. Therefore, in this semifinished assembly in which the stationary scroll is meshed with the orbiting scroll which is placed on top of the frame with an Oldham ring sandwiched in between, it may occasionally be impossible to sufficiently incline the rotary shaft with respect to the rotary shaft bearing and the secondary shaft end bearing in a reliable fashion in step (b) above. For this reason, the fixing point obtained in step (f) of the positioning method of Japanese Patent Application Publication No. 2001-221170 may not a correct fixing point where the stationary scroll should be fixed for forming a series of pockets between the scroll wraps of the stationary scroll and the orbiting scroll.